1. Field of the Invention
The present invention relates to a useful method for producing a high quality and sound copper alloy ingot while suppressing casting defects, segregation and oxide content.
2. Description of the Prior Art
A vacuum melting casting method has hitherto been employed for producing a copper alloy ingot, which is free from oxides and contains a reduced number of pinholes caused by dissolved oxygen or dissolved hydrogen. In addition, various attempts have been made, which include directional solidification under vacuum or in an argon gas atmosphere, in order to produce a sound ingot having less shrinkage cavities, segregation of components and other defects. The shrinkage cavities, which are usually caused during solidifying the molten metal, include macroscopic shrinkage cavities (e.g., center shrinkage cavity and final shrinkage cavity) and microscopic shrinkage cavities (e.g., shrinkage cavity observed in grain boundaries under a microscope). The conventional melting casting techniques commonly employ such procedure as, after the copper alloy material is molten in a crucible, a molten metal is poured into another container (casting mold) and then cooled to thereby solidify the molten metal.
However, the above conventional methods for melting and casting a copper alloy have a variety of problems, especially because there is provided the step of pouring the molten metal into the casting mold. The problems includes poor workability and productivity, complicated operations required to control the molten metal temperature during the pouring step, the low cooling efficiency of the casting mold leading to greater feeding and higher equipment investment, thus resulting in higher producing cost. When the material is poured or molten in air rather than under vacuum or in an argon gas atmosphere to prevent these problems, there arises a problem that oxides are entrained in the step of pouring or melting the molten metal.